A Metro-North passenger train lies on its side Dec. 1 after derailing on a curved section of track in the Bronx borough of New York. / Mark Lennihan, AP

by Gary Stoller, USA TODAY

by Gary Stoller, USA TODAY

An accident occurs, on average, once every two days on the nation's passenger and commuter trains, according to a USA TODAY analysis of federal rail data.

The frequency of accidents may sound alarms about lack of safety - particularly after a Metro-North train derailment in December that killed four passengers and injured 77 passengers and eight Metro-North employees in the Bronx, N.Y.

The statistics also show, however, that the railroads carry more than 550 million passengers annually, and yearly accidents and derailments for Metro-North, Amtrak and all passenger and commuter railroads combined have decreased sharply during the past 11 years.

Federal Railroad Administration (FRA) data reveal that 27 railroads reported 2,259 accidents, including 779 derailments and 101 collisions, during the past 11 years, according to the analysis. Fifty passengers were killed and 2,685 injured in the accidents, which include trains with only employees aboard.

The analysis included only railroads under the jurisdiction of the FRA, which regulates all passenger, commuter and freight railroads. Subways and other trains, such as the Chicago Transit Authority train that derailed and injured 32 people at O'Hare airport Monday, are regulated by the Federal Transit Administration.

Amtrak trains, which are under FRA jurisdiction, were involved in 988, or 44%, of the total number of passenger and commuter rail accidents from Jan. 1, 2003, through Dec. 31, 2013, and passengers were aboard for about half of them, according to USA TODAY's analysis.

In 2003, Amtrak trains were involved in 103 accidents, compared with 57 last year.

Trains of New Jersey's NJ Transit and the New York metropolitan area's Metro-North Railroad account for the highest accident percentages after Amtrak during the past 11 years.

According to the National Transportation Safety Board, the Metro-North train in the Bronx accident was traveling 82 mph before it derailed on a 30-mph curve. The board hasn't determined whether human error or faulty equipment caused the high speed.

The Metro-North accident and thousands of others during the past 11 years are a cause of concern, says Jim Hall, former NTSB chairman.

"The statistics speak for themselves," he says. "Passengers should be concerned about their safety."

The FRA says train travel is safe.

"The last two years were the safest periods in the rail industry's history," the FRA says in written answers to USA TODAY questions. "Since 2004, passenger/commuter train accidents have declined by more than 44%, derailments by 41.7% and collisions by 50%, even as passenger rail traffic and ridership has increased."

Improved accident records and a large number of passengers carried without incident may not address safety problems.

The FRA said a combination of Metro-North's "strong emphasis on on-time performance" and increased train activity "appears to have led managers and supervisors to allow inspections, maintenance and employee training to lapse."

USA TODAY's analysis - which included FRA data, government documents and interviews with safety experts and railroad officials - reveals the most prevalent causes of accidents of Metro-North and Amtrak trains during the past 11 years were track problems.

Besides their own tracks, commuter and passenger railroads operate on many miles of track maintained and used by freight railroads.

"The condition of the track is deplorable," says Ben Saunders, a lawyer who has represented many railroad workers injured on the job.

Saunders says track ties are often old and rotten, and passenger trains operate at higher speeds on tracks generally used by freight trains at lower speeds.

The FRA says track conditions "are safer than at any point in the industry's history." In 1978, there were 4,780 track-caused accidents of passenger, commuter and freight trains, compared with 554 in 2013, the agency says.

At a House hearing on oversight of passenger and freight rail safety last month, FRA Administrator Joseph Szabo cited a long list of industry safety improvements and said there have been "significant reductions in all types of accidents since 2008." Szabo said, "Rail is a particularly safe form of transportation."

In December, the Government Accountability Office reported that safety inspectors of the FRA, a small government agency, "have the ability to inspect less than 1% of the federally regulated railroad system."

The FRA does receive some inspection assistance from states, and railroads do their own inspections.

Amtrak, which carried 33 million passengers last year, did not answer USA TODAY's questions about its accident record. In a written statement, Amtrak said, "Safety is a priority," and it works with freight railroads "on safety practices." Other railroads own 72% of the miles of tracks on which Amtrak trains operate, Amtrak said.

Metro-North spokesman Aaron Donovan says, "The safety of our passengers, employees and the public at large is Metro-North's top priority."

Donovan says Metro-North has taken numerous steps to improve safety after the accident in December and a derailment in Bridgeport, Conn., last May. In the Bridgeport incident, a train derailed and struck another train, injuring 120 passengers and 10 Metro-North workers.

Since those incidents, Donovan says, Metro-North has, among other improvements, improved the signal system at five curves of track, reduced speed limits at 33 locations and created a management position focusing solely on safety.